The present invention relates in a general way to devices for cardiac ventricular assistance, commonly known as VADs (an acronym for Ventricular Assist Device).
Devices of this kind (such as those described, for example, in EP-A-0 728 488 and EP-A-0 728 489) are designed to be used to assist a heart muscle by replacing the left ventricle which is no longer capable of carrying out an adequate action of pumping the blood to the circulatory system.
For this purpose, the device is connected in such a way as to act between the left atrium and the aorta, producing a connection arranged in fluid dynamic terms in parallel with the natural circuit, orxe2x80x94in a connection device which tends to be preferredxe2x80x94in a position interposed between the apical region of the left ventricle and the aorta, and therefore in series with the natural circuit.
Other systems of connection between the VAD and the cardiovascular system have been and can be proposed (for example what is known as the xe2x80x9cWindkesselxe2x80x9d systemxe2x80x94F. Unger et al., Med. Instrum. 1976, vol. 10, p. 256), and could be reconsidered in the future.
The devices in question are at present mainly used as what is known as a bridge to transplantation, in other words as an aid designed to maintain circulatory function in a patient waiting for a heart transplant operation. However, they are also suitable for use in a form of long-term assistance and it is expected that this application may become widespread in the near future.
More recently, an application as what is known as a bridge to recovery has been assuming a degree of importance.
In this case, the ventricular assistance device is designed to be used for a limited period (for example 3-4 months), so that it temporarily replaces the left ventricle which in the meantime can recover, possibly as the result of suitable treatment, a level of function sufficient to enable the patient to return to substantially normal living conditions after the removal of the VAD.
This application is of the xe2x80x9ctherapeuticxe2x80x9d type, in other words it would enable the patient to be cured and subsequently allow him to return to a substantially normal life (a good quality of life). On the other hand, the long-term use of a VAD (or a complete artificial heart) as a fixed prosthesis makes the patient completely and permanently dependent on the device and on the corresponding supply and control systems, with significant restrictions on his independence and quality of life.
The results obtained up to the present time are very promising; however, they have revealed the highly critical naturexe2x80x94for the purposes of achieving a truly satisfactory end resultxe2x80x94of the method of controlling the VAD, in other words of the possibility or otherwise of synchronizing the action of the VAD with that of the natural heart, and of the management of what is known as the weaning phase, in other words the phase in which, after having been totally replaced by the ventricular assistance device in its function, the recovering ventricle is gradually returned to the performance of its function, with the objective of achieving the removal of the ventricular assistance device when the ventricle has recovered a satisfactory level of function.
For example, the paper by M. Loebe et al., xe2x80x9cVentricular assistance for recovery of cardiac failurexe2x80x9d, published in Current Opinion in Cardiology, 1999, 14:234-248, describes a weaning method which essentially proposes the operation of the ventricular assistance device at a fixed frequency and gradually reducing this frequency as the weaning proceeds. The main drawback of this solution is that the frequency of intervention of the device, being fixed, and therefore generally different from that of the natural heart, can give rise to situations in which the ventricular assistance device comes to carry out its pumping action in opposition to the pumping action which is beginning to be carried out again by the natural ventricle. In these conditions, the natural ventricle is subjected to a high fluid dynamic load: in practice, the natural ventricle can be in systole and attempt to pump the blood located within it while the ventricular assistance device is also in systole. Although accidental, this event can have a rather negative effect on the execution of the weaning phase, and may even prevent its success.
The paper by F. Miyawaki et al., xe2x80x9cRecovery-Directed Left Ventricular Assist Device (RDLVAD) May Promote Cardiac Recoveryxe2x80x9d, presented at the XIIth ISAO/XXVIth ESAO Joint Congress at Edinburgh, Aug. 3-6, 1999, describes a ventricular assistance device consisting of a valved apical duct, a ventricular load control chamber of the yielding type, and a pump. The device allow the natural ventricle to eject the blood into the aforesaid chamber, whose degree of yield can be selectively adjusted. It is thus possible to produce fluid dynamic loads for the natural heart which are adjustable, and which may be considerably lower than the load corresponding to the aortic pressure in the recovery phase and gradually increase in the weaning phase; the function of pumping blood from the aforesaid yielding chamber to the aorta continues to be carried out by the pump of the device.
Regardless of any other consideration, this solution has the drawback of requiring the presence of at least one additional element (the bag or chamber with adjustable yieldingness) which has to be designed to be locatedxe2x80x94and therefore implantedxe2x80x94in a position interposed between the apex of the heart and the VAD.
The object of the present invention is to provide a solution which can enable a weaning stage to be carried out according to principles which, on the one hand, are optimal in terms of the recovery of the function of the natural ventricle, and, on the other hand, make it unnecessary to implant elements additional to the elements forming the cardiac ventricular assistance device.
According to the present invention, this object is achieved by means of a device having the characteristics claimed in a specific way in the following claims.
The invention also relates to an accessory, considered as an independent element, capable of being coupled to a ventricular assistance device for the application of the solution according to the invention, and also to the corresponding procedure for using the device.
The invention will now be described, purely by way of example and without restrictive intent, with reference to the attached drawings, in which: